1. Field of the Disclosed Embodiments
The disclosed embodiments relate to Light Emitting Diode (“LED”) drivers using low voltage power corrected input that deliver low voltage direct current (“de”), at substantially constant current.
2. Background of the Related Art
Low voltage AC tracks are desirable because the tracks are easy to install and are safe to touch. The benefits are easy to appreciate for “do-it-yourself” type individuals and are suitable for installation in low lying areas such as residential gardens where children and pets play. Low voltage halogen fixtures which are typically powered by these low voltage tracks have challenges. The halogen bulbs are relatively expensive, have short life spans and are relatively hot. The industry desires LED fixtures for placement in the low voltage tracks which have extremely long life spans, are not nearly as hot when properly powered and are more energy efficient.
Challenges to be overcome with LED lighting include that each diode in an LED array configuration, as can be found in a single fixture, requires three to four volts-DC (“VDC”) to light. Thus, a multi-die LED array on one fixture can quickly exceed the supplied low voltage, preventing power from flowing through the LED array. In addition, LEDs can burn out if exposed to current in excess of their rated current. Moreover, if dimming is desired, reducing the available voltage can cause LED flicker.
On the other hand, power factor correcting has become a concern of consumer side usage. Power factor correcting is widely used in offline power supplies and drivers for 120V and up. When using standard incandescent light, the power factor is always 100%, but this is not the case with LEDs.
New power regulations, like Energy Star, are demanding power factors over 90%. A reduced power factor is sensed when a power company's transformers become overloaded due to mismatching electrical characteristics at the consumer side load. Specifically, the phase difference between voltage sensed at the consumer side as compared with current absorbed by the consumer side load is mismatched. Such mismatching causes an improper electrical pull on the supply side.
A power company charges commercial consumers for resulting losses, though regulations prohibit a power company from directly charging residential consumers. Nonetheless, power losses result in an increased in cost for all consumers, both residential and commercial.